OFDM transceiver structure with time-domain scrambling

Abstract

A method and transceiver for wireless multicarrier communications. At the transmitter side, conventional OFDM symbols, after inverse fast Fourier Transform, are scrambled in time domain and then guard-interval (GI) inserted, up-converted at the carrier frequency for transmission. At the receiver side, after GI removal and frequency domain channel equalization, the received signal is transformed into time-domain by inverse fast Fourier Transform. The time-domain equalized signal is descrambled in time domain and then transformed back to the frequency domain before it is rate-matched, demodulated and decoded. This time-domain scrambling and descrambling method can be used in a wireless OFDM system such as WLAN, cellular OFDM, and MC-CDMA.

1. A method of frequency division multiple access communications wherein a signal indicative of a plurality of information bits are encoded and modulated into a plurality of coded symbols, and the coded symbols are transformed into a further signal in time-domain, said method comprising:
 scrambling the time-domain coded symbols to provide a scrambled coded signal; and 
 appending the scrambled coded signal as redundancy data in a form a guard interval to provide a data stream with the guard interval for transmission. 
 
     
     
       2. The method of  claim 1 , wherein the data stream is received in a receiver and wherein the received data stream is guard interval removed, converted into frequency-domain and equalized to provide an equalized frequency-domain signal, said method further comprising:
 converting the equalized frequency-domain signal into a time-domain signal thereby providing an equalized time-domain signal; 
 descrambling the equalized time-domain signal to provide a descrambled time domain signal; and 
 converting the descrambled time-domain signal into a further descrambled signal in the frequency domain. 
 
     
     
       3. The method of  claim 2 , wherein the received data stream is converted into the frequency domain by a fast Fourier transform (FFT) operation. 
     
     
       4. The method of  claim 2 , wherein the equalized frequency-domain signal is converted into the time domain by an inverse fast Fourier transform (IFFT) operation, and the descrambled time-domain signal is converted into the further descrambled signal in the frequency domain by a fast Fourier transform (FFT) operation. 
     
     
       5. The method of  claim 1 , wherein the coded symbols are transformed into the further signal in the time domain by an inverse fast Fourier transform (IFFT) operation. 
     
     
       6. The method of  claim 1 , further comprising
 up-converting the data stream with the guard interval at a carrier frequency for transmission over a frequency selective fading channel. 
 
     
     
       7. A transmitter for use in frequency division multiple access communications wherein a signal indicative of a plurality of information bits are encoded and modulated into a plurality of coded symbols and the coded symbols are transformed into a further signal in time-domain, said transmitter comprising:
 a scrambling module, responsive to the further signal, for providing a signal stream indicative of scrambled time-domain coded symbols; and 
 an appending module, responsive to the signal stream, for appending the scrambled coded symbols as redundancy data in a form of a guard interval to provide a data stream with the guard interval for transmission. 
 
     
     
       8. The transmitter of  claim 7 , wherein the guard interval has a length which is greater than a maximum delay spread. 
     
     
       9. A receiver for use in a frequency division multiple access communications system, the system having a transmitter which comprises:
 means for encoding and modulating a signal indicative of a plurality of information bits into a plurality coded symbols; 
 means for providing a further signal in time domain indicative of the plurality of coded symbols; 
 means for scrambling the further signal to provide a scrambled signal; 
 means for appending the scrambled signal as redundancy data in a form of a guard interval to provide a data stream with the guard interval for transmission; and 
 means for transmitting the data stream with the guard-interval wherein the data stream received in the receiver is guard-interval removed, converted into frequency-domain and equalized to provide an equalized frequency-domain signal, said receiver comprising: 
 a first module for converting the equalized frequency-domain signal to an equalized time-domain signal; 
 a second module for descrambling the equalized time-domain signal to provide a descrambled time-domain signal; and 
 a third module for converting the descrambled time-domain signal into a further descrambled signal in the frequency domain. 
 
     
     
       10. The receiver of  claim 9 , wherein the data stream received in the receiver is guard-interval removed, converted into the frequency-domain and then equalized by a one-tap channel equalizer to provide the equalized frequency-domain signal. 
     
     
       11. The receiver of  claim 9 , wherein the first module comprises an inverse Fourier transform operation for converting the equalized frequency-domain signal to the equalized time-domain signal, and the third module comprises a Fourier transform operation for converting the deserambled time-domain signal to the further descrambled signal in the frequency domain. 
     
     
       12. A frequency division multiple access communications system, comprising:
 a transmitter including:
 a first module for encoding and modulating a signal indicative of a plurality of information bits into a plurality coded symbols to provide a further signal indicative of the plurality of coded symbols; 
 a second module for converting the coded symbols into frequency-division multiplexed symbols in time-domain; 
 a third module for scrambling the frequency-division multiplexed symbols in time domain to provide a scrambled signal, 
 a fourth module for appending the scrambled signal as redundancy data in a form of a guard interval to provide a data stream with the guard interval for transmission, and 
 a fifth module for transmitting the data stream with the guard-interval signal; and 
 
 a receiver for receiving a data stream, the receiver including:
 a first module for removing the guard interval in the data stream to provide a guard-interval removed signal; 
 a second module for converting the guard-interval removed signal into a frequency-domain signal; 
 a third module for equalizing the frequency-domain signal to provide an equalized frequency-domain signal; 
 a fourth module for converting the equalized frequency-domain signal into an equalized time-domain signal; 
 a fifth module for descrambling the equalized time-domain signal to provide a descrambled time-domain signal; and 
 a sixth module for converting the descrambled time-domain signal into a further descrambled signal in frequency domain. 
 
 
     
     
       13. The communications system of  claim 12 , comprising a wireless local area network (WLAN). 
     
     
       14. The communications system of  claim 12 , comprising a cellular orthogonal frequency division multiplexing (OFDM) system. 
     
     
       15. The communications system of  claim 12 , comprising a multi-carrier code division multiple access (CDMA) system. 
     
     
       16. The communications system of  claim 12 , comprising a digital subscriber line (DSL) system. 
     
     
       17. The communication system of  claim 12 , comprising a digital broadcasting system. 
     
     
       18. A component in a frequency division multiple access communications system, comprising:
 a transceiver operatively connected to an antenna, the transceiver comprising:
 a transmitter including:
 a first module for encoding and modulating a signal indicative of a plurality of information bits into a plurality coded symbols to provide a further signal indicative of the plurality of coded symbols, 
 a second module for converting the coded symbols into frequency-division multiplexed symbols in time-domain; 
 a third module for scrambling the frequency-division multiplexed symbols in a time domain to provide a scrambled signal, 
 a fourth module for appending the scrambled signal as redundancy data in a form of a guard interval to provide a data stream with the guard interval for transmission, and 
 a fifth module for transmitting the data stream with the guard-interval signal; and 
 
 a receiver for receiving a data stream via the antenna, the receiver including:
 a first module for removing the guard interval in the data stream to provide a guard-interval removed signal; 
 a second module for converting the guard-interval removed signal into a frequency-domain signal; 
 a third module for equalizing the frequency-domain signal to provide an equalized frequency-domain signal; 
 a fourth module for converting the equalized frequency-domain signal into an equalized time-domain signal; 
 a fifth module for descrambling the equalized time-domain signal to provide a descrambled time-domain signal; and 
 a sixth module for converting the descrambled time-domain signal into a further descrambled signal in a frequency domain. 
 
 
 
     
     
       19. The component of  claim 18 , comprising a user equipment (UE). 
     
     
       20. The component of  claim 18 , comprising a mobile terminal.